CHAPTER 4 



THE MOVEMENT OF CILIA 

 AND FLAGELLA 



The structure of cilia is well known, and various parts are 

 consistently present. It is proposed in this chapter to describe 

 the form of beat of cilia and flagella, to attempt the allocation of 

 functions to the component parts of these organelles, and to 

 discuss the means by which these functions are carried out. The 

 action of many factors on the activity of cilia has already been 

 described, and knowledge gained from these studies will be 

 incorporated into discussions here. Some of the ideas presented 

 here are purely hypothetical, and it is hoped that the reader will 

 be able to distinguish facts from speculation. 



1. The Form of Beat of Flagella 



It seems unlikely that the familiar pattern of flagellar beating 

 in which the organelle takes the form of a sine wave is often found 

 anjrwhere but in theoretical discussions. In all cases examined 

 the pattern seems to depart from this ideal in at least some 

 details. In fact, few flagella have been studied in sufficient detail 

 for adequate description of their movement, with the exception 

 of studies on the sperm tails of the sea urchin and bull by Gray 

 (1955, 1958), in which the sea urchin was found to approach 

 nearer to the sine wave pattern. Protozoan flagella normally 

 show a modified beating pattern on account of their position and 

 mode of functioning, and m.ust be. considered separately. 



Gray (1955) established that the bending waves of the flagellar 

 tail of the sea urchin sperm take place in a single plane. In sea 

 urchin sperm tails that beat symmetrically, waves of bending 

 arise at the head end of the tail and pass towards the tip, moving 

 down opposite sides of the tail in strict alternation to give the 

 pattern shown in PI. XV a, b and c. The tail is somewhat 

 longer than the length of one cycle of the sine wave bending 



127 



